Epstein-Barr virus (EBV)is etiologically associated with many cancers, including nasopharyngeal cancer, Hodgkin's and non-Hodgkin's lymphoma, and Burkitt's lymphoma. The virus remains in a state of limited gene expression in all EBV-associated tumors and in B cells of healthy infected persons. Reactivation into the viral lytic cycle is required for cell to cell spread and transmission among individuals. The bZIP protein, ZEBRA, encoded in the EBV BZLF1 gene, mediates the switch between latency and lytic cycle. The global objective of the proposal is to understand ZEBRA's mechanism of action and regulation of expression. Experiments concerning the function of ZEBRA will analyze consequences of mutations in ZEBRA's basic domain on conformation, protein-protein interactions and capacity to alter chromatin on target promoters. The role of phosphorylation in regulation of ZEBRA's action, particularly as a repressor of late viral promoters will be investigated. Experiments that explore control of expression of BZLF1 will address the question whether open chromatin configuration is sufficient to activate Zp, the BZLF1 promoter. The novel hypothesis that CpG methylation downstream of Zp may regulate BZLF1 expression will be pursued. The potential role of cellular Oct 1 as an inhibitor of Zp autostimulation will be examined. The proposed experiments, utilizing molecular genetics and biochemistry, are integrated into the biology of the virus and address several seminal unresolved issues about the pathogenesis of this human cancer virus.